How Tears Go 'Pac-Man' To Beat Bacteria

Tears contain an enzyme that eats bacteria the way Pac-Man eats Power Pellets.

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Originally published on January 23, 2012 3:39 pm

The mystical healing properties of tears are invoked in fairy tales and fantasies from Rapunzel to Harry Potter. So it may surprise you to hear that tears really are pretty powerful, on the microbial level at least.

In 1922, a few years before he won the Nobel Prize for his discovery of penicillin, bacteriologist Alexander Fleming discovered in human tears a germ-fighting enzyme which he named lysozyme. He collected and crystallized lysozyme from his own tears, then wowed contemporaries at Britain's Royal Society by demonstrating its miraculous power to dissolve bacteria before their very eyes.

"That's a seriously bodacious experiment," Gregory Weiss, professor of molecular biology at the University of California, Irvine, tells Shots. Weiss is co-author of a paper on a modern-day bodacious experiment that for the first time reveals details of how lysozyme works.

"People had always wondered, did 100 molecules gang up and attack a bacterium?" says Philip Collins, a physics professor at Irvine who joined the interdisciplinary research team. "What we've shown is that just one molecule of enzyme is enough."

How is that possible? Well, each molecule is essentially a set of voracious jaws that latches on to microbial invaders, starts chewing and doesn't let go. "The enzyme opens and closes almost like a Pac-Man mouth as it chomps away," Collins says, which means it can chew through bacterial cell walls as easily as scissors slice through paper.

"This tells us that the enzyme opens huge, gaping holes in the bacteria, which cause the bacteria to explode," Weiss says.

Each tear you shed contains an army of these enzymatic Pac-Men, ready to chase down and gobble up germs before they infect the sensitive tissues around your eye. But in order to study their motion up close, the researchers had to keep one of the molecules still. And to do that, they relied on some very tiny technology: carbon nanotubes.

The team attached a lysozyme molecule to a nanotube, using an amino acid as a tether. Then they passed an electric current along the tube, essentially turning the molecule into a very tiny transistor. When the molecule sprang into action, each chomp of its jaws produced a blip of electrical activity, like the dit-dit-dit of a telegraph.

That signal was like "a microphone that allowed us to listen in on the enzyme's activity," Collins says.

The researchers plan to use this technique to study many other molecules. Down the road, everything from DNA, to pharmaceuticals, to cancer biomarkers could be incorporated into similar biological transistors.

"We're building circuits that are hybrids between biology and technology," Weiss says. "It's fun because we're building a new field. It's something that hasn't been done, and that's what makes it exciting."